It appears Google has somehow managed to crawl and index the /user/password page (according to Google Search Console) - is it possible to set it to "noindex" (without using Node noindex)?

Accepted answer

Open your theme folder,
the mytheme.info file lists the scripts (and CSS) connected to the theme:
scripts[] = myscript.js 
(see docs https://docs.backdropcms.org/creating-themes)
If there are no scripts, add this line,
create myscript.js, paste the code into it:

$(document).ready(function() {
         console.log('This message will be displayed in the console if the script is connected correctly'); 
         // Any code will be here 
});

Clear cache.

For an example, see the structure
/core/themes/basis/basis.info

Most helpful answers

I`m use JS:

var path = window.location.pathname.substring(1);
var noindex = ['user','search'];
noindex.forEach(el => {
    if (path.indexOf(el) > -1) {
        setNoindex();
        return;
    } 
});
function setNoindex() {
    var meta = document.createElement('meta');
    meta.name = 'robots';
    meta.setAttribute('content', 'noindex');
    document.getElementsByTagName('head')[0].appendChild(meta);
}

Comments

I`m use JS:

var path = window.location.pathname.substring(1);
var noindex = ['user','search'];
noindex.forEach(el => {
    if (path.indexOf(el) > -1) {
        setNoindex();
        return;
    } 
});
function setNoindex() {
    var meta = document.createElement('meta');
    meta.name = 'robots';
    meta.setAttribute('content', 'noindex');
    document.getElementsByTagName('head')[0].appendChild(meta);
}

Thanks for the suggestion, but I don't know where to put that.

Since I'm using a sub-theme of Snazzy, it would go in the sub-theme as a new file?

Neither Snazzy or snazzytoys currently have this file - snazzytoys is set as the default theme in Backdrop.

Open your theme folder,
the mytheme.info file lists the scripts (and CSS) connected to the theme:
scripts[] = myscript.js 
(see docs https://docs.backdropcms.org/creating-themes)
If there are no scripts, add this line,
create myscript.js, paste the code into it:

$(document).ready(function() {
         console.log('This message will be displayed in the console if the script is connected correctly'); 
         // Any code will be here 
});

Clear cache.

For an example, see the structure
/core/themes/basis/basis.info

@Enthusiast - Thank you for your help. I have read through the doc you linked to and now have a slightly better understanding of what is happening.

For a long time I used ready-made themes for my websites, or used theme generation software, I thought that making themes myself was too difficult for me.

When I decided and figured out this issue, it turned out to be not so difficult. Now I can copy the design of any website, I can satisfy any design requirements of clients. I freed myself from dependence on ready-made themes.

CSS, JS (Jquery), little PHP, all this turned out to be very entertaining, I work with pleasure. Therefore, I advise everyone: don’t stand still, move forward, don’t be afraid to learn something new. You can do what others can do.